The invention is directed to the mechanical compressive shrinkage of a specific fabric material, namely gauze bandage material utilizing a two-roll, differential speed compactor of the general type typified by the Eugene Cohn et al U.S. Pat. No. 3,015,145. In the manufacture of gauze bandages, it has become the practice to subject the woven gauze material to a substantial pre-shrinking operation, in order to achieve improved bandage characteristics for certain purposes. Principally, such a pre-shrinkage procedure has involved so-called slack mercerizing of the gauze, which is typically constructed of 100% cotton yarns, assembled in a loose, open weave. Slack mercerizing, while resulting in a functional end product, has certain unavoidable disadvantages. Among these is a relatively slow processing speed. In this respect, the slack mercerizing process involves impregnating the gauze fabric with a caustic (sodium hydroxide) solution, permitting the fabric to relax, and then washing and drying the fabric. The mercerizing chemicals constitute a water pollutant and accordingly present a disposal problem. Moreover, slack mercerizing inherently involves shrinkage in both the length and width direction, whereas in general it is the length shrinkage that is the sought-after characteristic.
Notwithstanding that many of the important disadvantages of the slack mercerizing process could at least theoretically be minimized or eliminated by mechanical lengthwise compressive shrinkage of the gauze fabric, such procedures have proved elusively difficult to achieve in actual practice, because of the need for significantly high percentages of lengthwise shrinkage, taken in conjunction with the thin, somewhat gossamer character of the gauze material. For example, overall lengthwise compressive shrinkage of at least 35% is desired, which effectively rules out stretchable belt types of compressive shrinkage equipment. On the other hand, with the fabric being constructed of cotton yarns of 30's - 40's count, utilizing typically around 20 threads per inch in the warp direction and 12 threads per inch in the filling direction, the individual webs of gauze material have little substance and present significant handling problems in roller-type shrinkage equipment, even where the gauze material is processed in multiple thicknesses.
In accordance with the present invention, it has been found that surprising and unexpectedly good compressive shrinkage results are able to be achieved in a two-roll, differential speed mechanical compactor when utilizing a specific combination of feeding and retarding rollers. In particular, the compressive shrinkage equipment is of the general type disclosed in the aforementioned Eugene Cohn et al U.S. Pat. No. 3,015,145. However, pursuant to the present invention, the just-described mechanical compacting machine has been modified to incorporate a specific combination of feeding and retarding rollers, which have been found through extended experimentation to be specifically and surprisingly effective in the processing of woven gauze bandage material.
More specifically, the present invention is based on the discovery that commercially successful mechanical compacting results may be achieved with woven gauze bandage material when the two-roll, differential speed compactor is modified so as to utilize, in combination, a retarding roller formed with a diamond knurl surface pattern of approximately 40 pitch and the opposing feed roller is formed with a straight knurl surface pattern of approximately 80 pitch. This specific combination of feeding and retarding roller surface characteristics has been found to produce effective and desirable results, whereas other combinations of roller surface characteristics that logically should have been effective were found to be either ineffective or unable to sustain production for a reasonable time.
The use of the combination 40 pitch diamond knurl on the retarding roll and 80 pitch straight knurl on the feeding roll has, for the first time, enabled gauze bandage material to be mechanically compressively shrunk to achieve a product which is competitive with the product of the older slack mercerizing process. At the same time, moreover, the mechanical compressive shrinkage procedure provides significant practical and cost saving advantages over the mercerizing procedure, so that it becomes a significantly more attractive process overall.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following description of a preferred embodiment and to the accompanying drawings.